Pilot valve



F. w. SCHNECK June 21, 1949.

PILOT VALVE 2 Sheets-Sheet 1 Original Filed Jan. 11, 1946 r lllll fl QQM. Z a ebb WW v INVENTOR. F. w. SCHNECK ATTORNEY June 21, 1949. F. w. SCHNECIZK 2,474,122

r PILOT VALVE Original Filed Jan. 11, 1546' .2 Sheets-Sheet 2 3/ Z/Q I 306 k 20 /5 30 20 29 1.; 10 22 9 25 4 22 25 255 4 a 30d 32 22 6 28 259 2; K 2 /3 Fe? 23 Y 25: I: 520 I7 d 24 25 ze PRESSURE TIME INVENTOR. F. W. SCHN ECK ATTORNEY Patented June 21, 1949 PILOT VALVE Frederick W. Schneck, Santa Monica, Calif., as-

slgnor to Bendix Aviation Corporation, South Bend, Ind., a corporation of Delaware Original application January 11, 1946, Serial No.

640,466. Divided and this application December 17, 1947, Serial No. 792,244

1 This invention relates to hydraulic valves of the pilot type and has particular application to pressure regulating valves for use in hydraulic power systems. The invention represents an improvement in pilot valves of the general type disclosed in the patent to W. C. Trautman, 2,320,763, issued June 1, 1943, and this application is a division of my application Serial No. 640,466, filed January 11, 1946.

An object of the invention is to provide a pilot valve having desirable operational characteristics that is relatively simple and inexpensive to manufacture.

Another object is to provide a practicable and inexpensive pressure regulating valve unit of pilot type.

Other more specific advantages and features of the invention will appear from the detailed description to follow which refers to the drawing.

Pressure regulating valves are commonly used in hydraulic power systems to maintain the pressure in the system between predetermined limits by connecting the output of the pump to the system when the system pressure drops below a predetermined lower limit and disconnecting the output of the pump from th system when the system pressure rises above a predetermined upper limit. Such a system is disclosed in the Trautman Patent 2,320,763, previously referred to. As shown in that patent, the output of the pump is connected through a check valve to the hydraulic system and is connected through a normally closed hydraulically actuated valve to the fluid reservoir, so that, when the latter valve opens, the pump can discharge directly back to the reservoir at low pressure and does not waste energy pumping fluid against a high head pressure. In the patent, the hydraulic actuated valve is controlled by a pilot valve which is responsive to the pressure in the system. The pilot Valve construction disclosed in the patent has been used extensively but has the disadvantage that although it opens suddenly, it closes gradually. This causes a corresponding slow closing of the hydraulically actuated valve, which is less desirable than a faster action,

The present invention represents an improvement over the system of the Trautman patent in that the pilot valve inherently operates with a snap action in both its opening and closing movements. Furthermore, this snap action is obtained without the use of mechanical contrivances, by so designing the valve that when it starts to open the pressure force tending to open it is immediately increased, and when it begins to 1 Claim. (Cl. 137153) close the pressure force opposing the closing force is suddenly decreased. These variations in the pressure forces tending to open the pilot valve are obtained by making the controlling pressure effective over a larger piston area after the valve has started to open than before it opened, and decreasing the effective piston area to which the pressure fluid is applied when the valve begins to close.

In the drawing: a

Fig. 1 is a plan view of a pressure regulator incorporating a pilot valve in accordance with the invention;

Fig. 2 is a vertical sectional view taken inthe plane 11-11 of Fig. 1;

Fig. 3 is a vertical section taken in the plane III-III of Fig. 1;

Fig. 4 is a horizontal section taken in the plane IVIV of Fig. 2;

Fig. 5 is a horizontal section taken in the plane VV of Fig. 3;

Fig. 6 is a schematic diagram showing the valve incorporated in a hydraulic system; and

Fig. 7 is a graph illustrating the operation of the valve.

The general construction and operation of a valve in accordance with the invention will first be described with reference to the schematic diagram of Fig. 6 and the graph of Fig. '7, after which an actual construction of the valve will be described with reference to Figs. 1 to 5, inclusive.

Referring to Fig. 6, there is shown a system including a valve Ill, a fluid reservoir H, a pump l2, and an accumulator l3. The pump I2 is adapted to pump fluid from the reservoir ll through a conduit l4 and deliver it through a pump output conduit 15 to the valve 10. An exhaust conduit I6 extends from the valve 10 back to the reservoir H, and a pressure conduit [1 extends from the valve III to the system to be supplied with pressure fluid, the accumulator I3 being floated on the pressure conduit H. The accumulator I3 is not always employed, its function being merely to equalize pressure variations in the pressure conduit 11 and to maintain the pressure in the conduit for a longer period of time when the pump I2 is not supplying the demand.

The function of the regulator valve I 0 is to maintain the pressure in the pressure conduit ll between predetermined limits by connecting the pump output conduit l5 directly-to th exhaust conduit l6 when the pressure in the conduit 11 exceeds a desired value and reconnecting the pump output 15 to the pressure conduit I! when the asrc, 12a

pressure valve drops below a predetermined value. It is to be assumed that the pump l2 runs continuously during operation of the system.

As shown in Fig, 6 the regulator valve id is in condition for delivering the fluid flow through the pump output conduit 5 to the pressure conduit ll. Thus the conduit 85 is connected to a valve passage 58, which in turn is connected by a check valve 22 with a valve passage 23 which is connected with the pressure conduit H. The passage i8 may also be connected to the upper end of a, cylinder l9 by a main poppet 20, and the upper end of the cylinder I9 is connected by a valve passage 2| to the exhaust conduit 16.

As shown in Fig. 6, the main poppet 20 is closed, so that the output of the pump l2 flows past the check valve 22 and through the passage 23 to the pressure conduit l1, gradually building up the pressure therein.

The pressure in the passage 23 is supplied through a branch passage 23a to the lower end of a. bore 24, containing a piston element 25 having a head 25a which is sealed with the bore 24 by a seal 25b. The piston element 25 has an axial passage 25c therein, the lower edge 25d of which constitutes a seat for a pilot p ppet 26, which is lightly urged against the seat 25d by a helical compression spring 21.

The upper end of the bore 24 merges into the lower end of a bore 28 of slightly larger diameter, and the upper end portion 25a of the piston element 25 is sealed with respect to the bore 28 by a seal 25f. The piston element 25 is urged downwardly by a helical loading spring 29, which is compressed between the upper end of the piston element and the upper end of the bore 28. The upper end of the piston passage 25c merges into the lower end of a bore 25g in the piston element,

,and a normally stationary stem 30 projects into the bore 259 and is sealed with respect thereto by a seal 30a. A stem 30 is supported at its upper end from the body of the valve and is retained against upward movement by an adjustable stop 3!, which is threaded into the valve body. A seal 3% prevents fluid leakage past the stem to the exterior of the body. The stem 30 has an axial passage 30c extending therein from its lower end and communicated at its upper end with the bore 28, which bore is in constant communication with the exhaust conduit it through a passage 2m. The lower end of the passage 30c constitutes a valve seat 3011 adapted to be closed by an auxiliary poppet 26a formed on the upper end of a stem 26b on the pilot poppet 26. The lower end or the bore 25g in the piston element 25 is communicated by radial passages 25h with the lower end of the bore 28, which is communicated by a passage 32 with the lower end of the cylinder I9, which contains a piston 34, which is connected by a stem 34a to the main poppet 20.

As the pressure in the passage 23 rises, due to the delivery of fluid therethrough from the pump output conduit l past the check valve 22, this pressure is applied through the passage 23a to the lower end of the bore 24 and is eiiective against the lower end of the piston element 25 and the pilot poppet 26, to urge them upwardly against the force of the loading spring 29. When the pressure reaches a predetermined value determined by the strength of the spring 29 and the position of the stationary stem 30, the auxiliary poppet 26a seats against the seat 3011, thereby breaking connection between the lower end of the cylinder l9 and the exhaust passage 2|. Previous to this time, the piston 34 was exthe pressure in the lower end of:the cylinder l9,

but it does prevent further upward movement of the pilot poppet 26. The fluid pressure acting against the pilot poppet 26 is no longer eiiective to urge the piston element 25 upwardly, and the latter remains stationary until the pressure in the passage 23a rises to a higher value such that the force created by this pressure against the annular lower end of the piston-element is sufiicientto alone overcome the spring 29. Thereupon, the seat 250'. is cracked away from the pilot poppet 26, permitting pressure.iluid to flow upwardly through the passage 250, the passages 25h and the passage 32, to the lower end of the cylinder I9, starting movement of the piston 34 upwardly to open the main poppet 20. Following cracking of the seat 25d away from the pilot poppet 26, the piston element 25 is moved rapidly upwardly to produce a wide opening between the pilot poppet 25 and the seat 25d, because of the fact that the pressure fluid admitted through the radial passa'ges 25h to the lower end of the bore 28 is effective against the annular face 25i of the large head portion 25a of the piston element, the diameter of which is larger than that of the lower head portion 25a of the piston element. Hence,

The sudden upward movement of the piston element 25 and consequent large openin between the pilot poppet 26' and its seat 25d produces a sudden rush of pressure fluid through passage 32 into the lower end of the cylinder l9, which suddenly opens the main poppet 20 wide. Thereafter, the output of the pump l2 flows directly through the passage I8 past the poppet 20 and through the exhaust passage 2| and the exhaust conduit l6 back to the reservoir, so that the load is removed from the pump.

Assuming that fluid is being withdrawn by the system from the pressure conduit H, the pressure therein and in the lower end of the bore 24 will gradually drop, following opening of the main poppet 20, and the piston element 25 is gradually returned to its lower position by the loading spring 29. Eventually, this return movement carries the seat 25d against the pilot poppet 28, thereby breaking the connection between the passage 23a and the passage 32 leading to the lower end of the cylinder i9. However, pressure fluid is trapped in the passage 25c, bore 259, passages 2'5h, the passage 32, and the lower end of cylinder l9, so that the piston 34 still holds the main poppet 20 open. Further downward movement of the piston element 25 following Contact of the seat 25d with the pilot poppet 25 is temporarily interrupted by virtue of the fact that the force of the pressure fluid in the-lower end of the bore 24 against the pilot poppet 26 then becomes eiiective against the piston element 25. However, when the pressure in the pressure conduit I I, passages 23, 23a, and the lower end of bore 24 reaches a lower predetermined value, the spring 29 is efiective to move the piston element 25 and the pilot poppet 26 downwardly, carrying the auxiliary poppet 26a clear of the seat 30d. Thereafter, the piston element 25 is moved suddenly, or snapped, into its-full lower position, be-

cause the opening of the auxiliary Poppet 25a away from the seat 30d releases the pressure fluid that was trapped in the lower end of the bore 28 and which was effective against the piston face 25:. The pressure in the passage 32 and the lower end of the cylinder I8 is therefore suddenly released, permitting the spring 200 to close the main poppet 20 and force the fluid delivered by to crackthe valve seat 25d away from the pilot poppet 25.

The operation of the system may be readily followed by means of the graph shown in Fig. 7, in which the curve 40 represents the pressure in the pressure line I1, and the curve 4| represents the pressure applied to the main valve actuating Piston 34.

The curve 40 shows the fluctuations of pressure in the pressure line I! when fluid is being withdrawn from the pressure line at a rate less than the capacity of the pump I2. Beginning at point 40a on curve 40, the pump is supplying fluid to the pressure conduit and the pressure therein rises at a uniform rate to point 40b, at which pressure the valve functions as described to open the main poppet 20 and by-pass the pump discharge directly back to the reservoir. Thereafter the pressure in the pressure conduit ll gradually drops to the point 400, at which value the main poppet 20 is again closed, and the cycle repeats.

Referring now to curve 4|, it will be observed that up to point 4|b the pressure applied to the lower end of the piston 34 is zero because the lower end of the cylinder I9 is connected through the passages 32 and 25h, bore 259, the passage 30c and the passage 2|a, directly to the exhaust passage 2|. At a point 4|a, the auxiliary poppet 26a closes on the seat 3011 and disconnects the lower end of the cylinder l9 from the exhaust passage 2|. However, this does not change the pressure of the fluid trapped in the passages connected to the lower end of cylinder l9.

At point 4|b the seat 2511 is cracked away from the pilot poppet 26 and is thereafter moved rapidly into fully open position in the manner previously described, causing the pressure acting against the lower end of the piston 34 to rise rapidly to point He, at which pressure the force of the pressure fluid on the piston 34 is sufficient to begin to open the'main poppet 20. After it once begins to open, the main poppet 20 opens rapidly, and the corresponding rapid movement of the piston 34 permitsrelativel rapid flow of fluid through the passage 250, the passages 2571. and the passage 32 into the lower end of the cylinder l9, causing a resulting pressure drop in the latter to the point 4|d on the curve 4|. Thereafter the pressure in cylinder l9 rises rapidly to the point Me on curve 4| and then declines gradually with the pressure in the pressure conduit IT, as represented by that portion of the curve 40 between points 40b and 400.

At a point 4| j, the return movement of the piston element 25 in response to reduction of the system pressure reseats the seat 25d against the pilot poppet 25, but this causes no change in the pressure below the piston 34. At point 4| 9 on curve 4|, the system pressure has been reduced sufliciently to again permit the piston element 25 to resume its downward movement, opening the auxiliary poppet 25a off the seat 30d, whereupon the piston-element 25 is snapped into its lower position, permitting the pressure under piston 34 to drop rapidly to zero, as indicated at point am on curve 4|, which results in the closing of the main poppet 20.

It is particularly to be noted that if the bore 28 were of the same diameter as the bore 24, the opening of the auxiliary poppet 26a off the seat 30d would not change the pressure forces acting on the piston element 25 in opposition to the spring 29, and the piston would not be snapped 'into its lower position following cracking of the auxiliary poppet 25a away from its seat 30d. Instead, the auxiliary poppet 26a would be moved very gradually away from the seat 30d, resulting in gradual discharge of fluid from the lower end of the cylinder l9 and resultant sluggish closing action ofthe main poppet 20. Likewise, if the bores 24 and 28 were of the same diameter, the cracking of the seat 25d away from the pilot poppet 25 would not change the pressure forces acting on the piston element 25, and the, latter would admit fluid only very gradually to the lower end of the cylinder I9, resulting in sluggish opening movement of the main poppet 20.

It is also to be noted that pressure fluid in the Y and close with fairly rapid movement in orderto respond quickly to pressure changes in the system and maintain the system pressure within the desired limits.

Figs. 1 to 5 inclusive disclose a practical valve construction incorporating the features of the valve shown schematically in Fig. 6. Corresponding elements in Figs. 1 to 5 bear the same reference numerals as Fig. 6.

Referring to Figs. 1 to 5 inclusive, it will be observed that the valve housing comprises: a body having an upper end closure cap 5| and a lower end closure cap 52, both of which caps are secured to the body 50 by screws 53 and 54. The upper and closure cap 5| functions to close the upper ends of bores 55 and 28. Bore 55 functions as a guide for the main poppet 20 and contains a restoring'spring 20a for the poppet 20. A sealing ring 51 is provided to effect a fluid seal between the bore 55 and the upper end cap 5|.

The bore 28 (Fig. 3) has been described with reference to Fig. 6. As shown in Fig. 3 the upper end of, this bore is sealed by a plug 51 having a sealing ring 58, the plug being retained against the sealing cap 5| by the loading spring 29. The plug 51 has a bore which guides the stem 30, the latter being sealed with respect to the bore 60 by the sealing ring 30b. The adjusting screw 3| is threaded through the end cap 5| and may 1 be locked in a desired position of adjustment by a lock nut 62.

The screw 3| provides for adjustment, within limits, of the pressures at which the valve operates, by varying the vertical position of the seat 30d in the lower end of stem 30. Obviously if the stem 30 is lowered, the auxiliary P pet 26a will contact the seat sea at a lower system prm separate. from the body 58. Thus the bore Edi in the body d isf'of uniform diameter throughout except at the lower end of the body 58 where it is counterbored. The tubular insert 66 is fltted at its upper end into the bore 2m and sealed with respect thereto by a sealing ring 85. Intermediate its ends, the insert 64 is provided with'an outwardly extending flange t? which extends into the counterbore 68 at the lower end of bore 285 and is held against the shoulder of the counterbore by a sealing ring 69, which is pressed against the flange 61 by the lower end cap 52.

The piston element 25 is also preferably made in two parts, one of which forms the lower head 25a and the other of which forms the upper head 25c. The head element 25a also preferably has a separate tubular seat element Ill which is inserted in the head 25a. and sealed with respect thereto by the same chevron-type seal 25b that effects the seal between the piston head 25a. and the bore 24. The chevron-type seal 25f, which effects a seal between the piston head 25c and the bore 28, also effects a seal between the separate head portion 25c and the main part of the piston 25.

It will be obvious from inspection of Fig. 3 that by removing the lower end cap 52, the tubular element 64 and all of its associated parts can be removed as a unit.

Referring to Fig. 2, the main portion of the cylinder I9 is formed in the body 50, and the lower end of the cylinder is constituted by the lower end cap 52, which is sealed with respect to the cylinder l9 by a sealing ring 12. Likewise, the chamber for the check valve poppet 22 is formed by a bore 13 in the body 50, which bore is in direct communication at its lower end with the passage 23, which is formed in the end cap 52. The passage 23 terminates in a threaded port 18, which is adapted to be connected to the pressure line H of Fig. 6. The pump output passage I8 is formed directly in the body 50 and terminates in a threaded port 15 adapted to be connected to the pump output conduit ii of Fig. 6. The exhaust passage 2| is likewise formed directly in the body 50 and terminates in a threaded port it adapted to be connected to the exhaust conduit I6 of Fig. 6.

It will be apparent that when the lower end cap 52 is removed, the piston 34 with its integral stem 34a can be removed from the cylinder l9, and likewise the check valve poppet '22 and its spring 2212 can be removed from the bore 13. It is also obvious that when the upper end cap 5! is removed, the main poppet 20 and its spring 20a can be removed (Fig. 2) and the filler block 51 and the spring 29 (Fig. 3) can be removed.

Although considerable variation in the relative diameters of the bores 24 and 28 can be tolerated, I found that a desirable snap action on closing and opening movements of the piston element 25 are obtained in a valve having the following dimensions:

Inches Diameter of bore 24 .75 Diameter of bore 28 .812 Diameter of bore 259.; .281 Diameter of piston passage 25c .130

It will be understood that some special situations may make it desirable to have faster valve action, in which case the bore 28 can be made 28, or the shoulder 25k should be larger.

It will be'noted that the passage through the bore 25c around the poppet stem 26b ofiers more resistance to fluid'flow than do the-passages 2572. This is desirable because the passage around the stem 25b restricts only the flow of pressure fluid from the passage 23a into the bore 259, and does not restrict the flow of exhaust fluid. If the passages 2571 were restricted, they would not only offer resistance'to flow of pressure fluid from the bore 259 into the bore 28, but would also offer resistance to the exhaust of fluid from the bore 28 to the bore 259. Some restriction to flow of pressure fluid past the poppet stem 26b is desirable to prevent too rapid opening of the main valve 20. On the other hand, it is desirable to permit relative free flow of exhaust fluid from the lower end of the cylinder I 9 through the passage 32, the passages 25h, and the passage 300 in order to permit fairly rapid closing of the main valve 20.

As herein disclosed, the pilot valve, main poppet and check valve are all incorporated in a single valve body in order to make a compact assembly. However, it is not necessary that the main poppet 20 and lts'actuating piston and cylinder and the check. valve 22 be incorporated in the same body with the pilot valve mechanism, and the prior Trautman Patent 2,320,763 referred to herein above discloses these elements as separate units. Where, in the claim, the pilot valve alone is claimed, the passages 2m, 32, and 23a. of Fig. 6 are referred to respectively as a low pressure port, a control port, and a high pressure port respectively, to simplify the claim.

Although for the purpose of explaining the invention, one particular construction thereof has been described in detail, numerous departures from the exact construction shown can be'made while still utilizing the advantages yielded by the invention, which is to be limited only to the extent set forth in the appended claim.

I claim:

A hydraulic control valve of the type described comprising: a body member having first, second, and third longitudinal passages therein, said first and second passages extending completely through said body, and said third passage extending into said body from one end; a first closure cap secured to said one end of said body and closing all three of said passages; a second closure cap secured to the other end of said body, and closing said first and second passages; said body member having a lateral high pressure port communicating with the inner'end of said third passage and with said second passage, and a lateral low pressure port communicating with said second passage at a point longitudinally displaced from said high pressure passage; a valve seat between the inner end of said third passage and said high pressure port; a check valve in said third passage adapted to close against said seat; said first cap having a discharge port therein communicating with the outer end of said third passage; a valve seat in said second passage between the high pressure and low pressure ports therein; a poppet valve in said second passage adapted to close against the high pressure side of'said seat therein; a piston in said second passage on'the other side of the seat therein; said first passage being connected intermediate its ends by a control passage in said body with said second passage at the outer end of the piston therein; said first passage being connected at one end by a passage in said first cap with said discharge port, and

being connected adjacent its other end to a pas-- REFERENCES CITED The following references are of record in the file of this patenti I UNITED STATES PATENTS Number Name Date Grant May 8, 1945 Schultz Jan. 22, 1946 Schultz July 16, 1946 MacDufl May 20, 1947 Schultz Aug, 24, 1948 

